WasiCaml 1.1

• bases on OCaml-4.12.1 and WASI-SDK 19
• support for using the tail call extension of WebAssembly
  (-enable-tail-call), PR#36.
• support for using the exception handing extension of WebAssembly
  (-enable-exception-handling)
• reworked the way exceptions are propagated. If the exception is
  raised in OCaml code, it is passed up by returning the special
  value 0 to the caller (which has to check for it). If the
  exception is raised in C code, it is using the special
  "wasicaml_try" / "wasicaml_throw" host functions that are expected
  to be available (unless you -enable-exception-handling, in which
  case native WebAssembly exceptions are used in this case).
  The upside of this change is a simplified code generation.
  The downside is that the backtraces contain less information.
  (PR#40)
• more local variables: it is now tried to keep the top N
  values of the stack in local variables. This gives the
  JIT engine more opportunities to optimize the binary code.
  However, more save/restore code is now also required,
  so the code is less compact. For this reason, a new
  -compact-code command-line option was added. (PR#39)
• switching to wasi-js as the npm package to implement
  WASI in nodejs.